Reducing the safety risks of aerating wastewater lagoons

Traditionally, water authorities and industrial enterprises in Australia have adopted surface aerators for water oxygenation at municipal and industrial wastewater treatment plants (WWTPs). A large percentage of these WWTPs are based on earthen lagoons, with aeration being the main energy consumer associated with the treatment processes.

Surface aerators exist in various forms. There are high- or low-speed ‘splasher’ types, draft tubes, ‘brush and blade’ or paddlewheel aerators. All have reasonable oxygen transfer efficiencies of around 1.5 kg O₂/kWh. The challenge lies in the position of these surface aerators — all sit or float on the surface of the water, requiring operators to ‘boat’ to them for maintenance. For units that require pontoons, there is a risk of capsizing in strong winds.

A different approach is to use a Venturi Aeration unit in conjunction with a self-priming pump. The pump draws water from the lagoon or tank, accelerates it through the aerator then pumps highly oxygenated water back into the lagoon. The aerator uses the Venturi effect to draw over 2.2 times more air than the volume of liquid pumped before intensely mixing the air and water in the unit’s oxidising zone.

In addition to delivering up to 1.86 kg of O₂/kWh, a major benefit is the reduced risk of work health and safety issues. Because all monitoring and maintenance is done on the bank of the lagoon or at the side of the tank, the risks associated with ‘boating’ to units or the risks associated with the use of overhead cranes to access them is eliminated.

Another advantage of aerating with this system is the installation simplicity. Some aeration upgrades to lagoons can take weeks or months to complete, along with the risks associated with working over polluted water. The Venturi Aeration system with pump only requires a slab at the side of the lagoon.

Image caption: Venturi Aerators with Gorman-Rupp self-priming pumps. Image credit: © Hydro Innovations.